richardson



May 1, 1951 A. D. RICHARDSON 2,550,720

SUSPENSION GALVANOMETER AND MAGNET ASSEMBLY Filed May 29, 1946 3Shaets-Sheet 1 FIG. 2.

IN VEN TOR. AR THUR D. RICHARDSON A T TORNEYS y 1951 A. D. RlCHARDSON2,550,720

SUSPENSION GALVANOMETER AND MAGNET ASSEMBLY Filed May 29, 1946 3Sheets-Sheet 2 FIG. 8. FIG. 9. FIG. FIG. /4.

2/ A .34 A 29 -.3a

286 FIG. /2. FIG. /5.

1 l4 l4 50 L- 48 I FIG. /3.

FIG. /Z 74 /4 I5 74 INVENTOR. ARTHUR 0. RICHARDSON A T TOR/VEKS y 1951A. D; RICHARDSON 2,550,720

SUSPENSION GALVANOMETER AND MAGNET ASSEMBLY Filed May 29, 1946 3Sheets-Sheet 3 FIG. /9

- INVENTOR.

ARTHUR D. RICHARDSON A TTORNE KS Patented May 1, 1951 SUSPENSIONGALVANOMETER AND MAGNET ASSEMBLY Arthur D. Richardson, Pasadena, Calif.,assignor to Consolidated Engineering Corporation, Pasadena Calif., acorporation of California Application May 29, 1946, Serial No. 673,111

5 Claims.

This invention relates to galvanometers of the type adapted to respondto alternating or oscillating voltages, and more particularly to thetype of laboratory and portable galvanometers used for recordingalternating voltage oscillations.

Galvanometers of this type have been in use for a considerable time inrecording cameras and the like. Such galvanometers commonly cornprise alightweight coil suspended between the poles of a magnet by means of apair of suspension wires or cords. The oscillating voltage to beindicated by the galvanometer is connected to the coil terminals so thatthe coil oscillates accordingly. A mirror attached to the suspensioncord oscillates according to the oscillations of the coil so that alight beam reflected from the mirror correspondingly oscillates back andforth on a surface against which it is directed. According to a commonpractice, such a galvanometer is often placed in a camera, usually witha number of other similar galvanometers, and a photo graphic film orpaper strip is moved while the oscillating reflected light beam is on itso that an oscillating line or trace is made on the photographicstrip'of the oscillation from the mirrors.

The principal object of my invention is to provide a galvanometer ofthis type which is of a simple, small and lightweight constructionproviding easy access to the component parts.

A related object is to provide such a galvanometer whose position may bereadily adjustable without disturbing the characteristics of thegalvanometer.

I carry out my invention by the provision of an extremely lightweightand narrow coil held in suspension between a pair of stretched wireswhich constitute the axis of rotary movement of the galvanometer coil. Isupport this galvanometer element within an elongated casing preferablyprovided with a removable side or cover so that the elements are open toinspection and removal and adjustment. 1 provide in close associationwith the galvanometer coil a pair of pole pieces extending beyond thesides of the casing and adapted to be engaged by a suitable pole magnet.The arrangement is such that adjustment for the tilt of the galvanometerassembly can be made without disturbing the magnetic circuit.

The foregoing and other features of my inven- Fig. 2 is a side elevationview in crosssection taken at line 22 of Fig. 1;

Fig. 3 is a top cross-sectional iew taken at line 3-3.of Fig. 2;

Fig. 4 shows a front view of a coil assembly used in the galvanometer;

Fig. 5 is a side view of the coil shown in Fig. 4;

Fig. 6 shows a front view, and Fig. '7 an end view of a detail used withthe coil shown in Figs. 4 and 5;

Fig. 8 shows the arrangement of' a mirror in relation to the coil, usedin the galvanometer;

Fig. 9 is an end view, and Fig. 10 an elevation view of a sleeve used inthe galvanometer;

Fig. 11 is an end view, and Fig. 12 an elevation view of another bushingused in the ga lvanometer;

Fig. 13 shows a spring used with the bushing of Fig. 12;

Fig. 14 shows a cross-section view taken at line I4|4 of Fig. 15; and

Fig. 15 shows a face view of a member associated with the bushing ofFig. 12;

Fig. 16 shows a magnet adapted to receive a plurality of thegalvanometers shown in Figs. 1 and 2; and

Fig. 17 is a cross-section view taken at line ll-i'l of Fig. 16;

Fig. 18 is an enlarged front elevation view in cross section, showingthe details of the upper portion of the galvanometer; and, I,

Fig. 19 is a cross section view taken at line l9--l9 of Fig. 18.

Referring to the galvanometer shown in Figs. 1 to 3, the instrumentcomprises a casing It in the form of a square 01' rectangular prismwhose length is many times greater than its cross-sectional dimension.The casing comprises an elongated back strip H and two side strips l2and i3. A cover 9 is adapted to be put on or taken off by'sliding it ingrooves Ho and 13a placed in side plates 12 and !3. There are fastenedthrough the sides l2 and I3 of the casing, a pair of .pole pieces [4 and15. These are rig idly fastened in position in the casingv in somesuitable manner so as to leave a narrow elongated gap 16 between the twopole pieces in a central location in the casing as shown in Figs. 2 and3.

There is suspended within this narrow gap be-- tween the pole pieces, anelongated coilf! "I of fine wire shaped to occupy a very smallcross-sectional area. This coil is shown enlarged and in better detailin Figs. 4 and 5. It is composed of a fine insulated wire, such as No.i8 enameled, or

3 even thinner, and may be on an arbor formed suitable for winding suchfine wire. The winding is preferably done in such a manner that the coilis substantially cylindrical in form with a circular cross-sectionhaving a diameter d. The wires forming this coil are preferably cementedtogether so that the coil maintains a rigid selisupporting form. Thelong dimension L may conveniently be about .5 and the diameter d in theneighborhood of .015 inch.

There is inserted inside each extremity of the coil a semi-circularmember in the form of a half disc 29 with its straight edge at the loopof the coil, as shown in Figs. 6 and 7. The half discs 28' arepreferably of insulating material to avoid danger of short-circuitingthe coil turns. For the purpose of suspending the coil in position inthe air gap Hi, there are provided thin suspension wires 2| and 22 ateach end of the coil, these suspension wires being looped through thecoil and inside the arcuate surfaces of the respective members 20. Thewires 2! and 22. may conveniently be a No. 49 wire rolled flat .0602 to.065 inch of gold or gold alloy. The ends 23 and 2d of the fine wireforming the coil ll are brought out loosely and preferably are loopedaround the respective loops'of the suspension wires 2! and 22, as shown.The loops of wires 2! and 22 are maintained by solder at positions 25and 26 respectively, and

the ends of wires 23 and 2 3 are also soldered at the same points,thereby making the wires 2! and 22, in effect, the terminals of thecoil.

= One of the wires, namely wire 2 l, has attached to it a small mirror2?. The mirror is rectangular in shape and its arrangement with wire 2iis shown more clearly in the enlarged view in Fig. 8. The wire 2i loopedat coil H and soldered at 25, has its two strands carried parallel fromthe solder point 25 to another solder point 28 close to theposition ofthe mirror. At point 28, the two strands of wire 2! divide, one of them,23a, being carried along one of the longer edges of the mir ror, and theother of them, 2817, being carried along the other long edge of themirror. At the opposite side of the mirror, the two separated strands28a and 281) are joined again at a solder pointZQ. At this point, onlyasingle strand of wire, 2!, is carried on up.

For the purpose of suspending this mirror and coil assembly withsuspension wires 2! and 22, centrally within the casing, there isprovided at one end of the casing a wire holding member 39 in the formof a cylindrical rod, and at the other end of the casing a compressionspring held within an insulator bushing 58, the wire 22 being hooked tothe spring. For the purpose of holding member 33, there is provided abushing 3|, preferably of a metal such as brass like the metal of thecasing. The bushing 3! is provided with a cylindrical sleeve portion 32which is fitted within an insulating bushing 33. The construction ofbushing 33 is shown in enlarged and greater detail in Figs. 9 and 16. Itcomprises a section of square cross-section 3-3 adapted to fit withinthewalls of the casing, and the outer end of it is'made cylindrical at 35where it protrudes through the opening in the end of the casing. Acylindrical hole 36 passes centrally through the bushing and thecylindrical sleeve portion 32 fits within the hole 36. In assembling thearrangement, an insulating collar or washer 37 is placed around thecylindrical portion 35 to separate the collar of the bushing 3i from thernetalliccasmg. I

-' The -outer portion of bushing 35 is provided with a small cylindricalbore through which the cylindrical rod 3! passes with a tight fit. Atthe inner edge of rod 36 there is provided a slot 39 into which the endof wire 2! is inserted and soldered firmly.

For the purpose of centering the wire 2| and of adjusting its effectivelength, there is provided a sleeve ll having a collar 82 at its innerend. This sleeve has a cylindrical shank which is adapted to slide witha tight fit in and out of the sleeve portion 32 of bushing 3i. Thesleeve M is formed with an open U-shaped slot Ma extending verticallythroughout the length of the slot to allow space for the wire ribbon 2!to lie in.

- Within the-slot at the base of the U is a protuberance 43 whichextends from the lower to the upper end of the slot. The protuberancetapers from both its upper and lower ends and is a maximum at a position4311. The protuberance extends longitudinally and the thickest point43a. is at the longitudinal axis so that the wire ribbon 2| in restingon this protuberance, is thereby centered in the casing. By slidingsleeve 4| in and out of the bushing, the position of the protuberance 13in the longitudinal or axial direction is changed, thereby effectivelyshortening or lengthening the effective length of wire 2| from the coill1. The'insulating bushing so located at the opposite end of the casingis illustrated in Figs. 11 and 12. It has outer side walls formed of asquare section to fit within the end of the casing; and it is providedwith a central bore 44 adapted to accommodate the compression spring 5iillustrated in detail in Fig. 13. For the purpose of retaining thespring in the bushing, the bushing is pro-. vided with an internalcollar 45 large enough to hold the spring but allowing sufficient roomfor the wire 22 to pass centrally through.

The end of wire 22 is soldered at $5 to a hook M which is hooked overthe outer end of the spring. For the purpose of holding thespring andinsulating bushing assembly in its proper position within the end of thecasing, there is provided a holding member Ali; in the form of ahorseshoe-shaped member as shown in Figs. 14

and 15. This is wedged within the casing so that it rests against thesides thereof.

The length of wire 22 is such that when hook i? is hooked over the endloop of spring M, the spring is compressed somewhat against member 48 sothat wires 2! and 22 are stretched with substantial tension. This isbrought about be cause there is sufficient tautness of ribbon 22 tocompress the spring which is within the cylindrical portion of thebushing 53, against the upper collar 45 of the bushing. This causes thecollar 45 to push against the wedged end of mem ber 38 to maintain it inits position. Furthermore, owing to the fact that the hook 4? is ofelectrical conducting material, it makes contactwith the. spring 5!,thereby putting the spring in circuit with the galvanorneter coil.Spring St is finished off with a straight end running across thediameter of the spring so that hook 4'1 can be adjusted sideways tobring the coil l1 midway between the pole pieces. To make connectionwith the spring there is soldered at the end 52 of the spring, asuitable connecting wire 53 which is insulated from the casing. Wire 53led through the galvanorneter casing, past the pole pieces l4 and l5,and is carried through the side 53 of the casing through an insulatingbushing 54; into the interior of a terminal casing 55. v

Terminal casing 55 is of insulating material such as fiber or Bakelite,or the like, and is fastened by screws and 51 to the galvanometercasing. Casing 55 has a rectangular or square cross-section and isprovided with an opening 58 running centrally through it. A collar 59 islocated within the opening and is provided with a shoulder 60 toaccommodate the head of a machine screw 6I. The end of the machine screwis threaded into the drilled and threaded end of a thick metallicconnecting slug 62 which is led into the terminal casing through opening64. The uninsulated end of wire 53 is carried through the insulatingbushing 54 and into the terminal casing 55 to a position between thelower edge of collar 59 and the upper end of connecting slug 52 so thatthe drawing up of the slug 62-by turning the screw binds the wire 53between the collar and the connecting slug. Connection to the slug maybe made by a sui able connecting means, such as a flexible insulatedconductor 52a, the end of which may be fastened into the slug 62.

When the galvanometer is assembled, the mirror 27 is located back of anopening 85 through wall I2 of the galvanometer casing and the face ofthe mirror faces the opening so that light coming through the openingwill shine on the mirror and be reflected from it back through theopening. A suitable lens 66 is held in a lens holder 6'! in front of theopening 65. For convenience,

the lens holder is provided with a second lens 68 of a different focallength from lens 66 so that if it is desired to use the second lensinstead of the first, the lens holder may be rotated on pivot 69 to putlens 63 into position in front of opening 65, instead of lens 65.

In a recording camera it is common to use a number of the galvanometersof the type which is described, and to place them as closely together aspracticable, so that all the galvanometers can make a record on a singlesheet of photographic paper or film which is drawn past them while theyare in oscillation, of their light traces. Furthermore, a magnetizingmeans is required for magnetizing the pole pieces I4 and i5. Anarrangement suitable for this purpose is shown in Figs. 16 and 17wherein there is shown a permanent magnet '15 of relatively large andheavy construction as compared with the galvanometer element. At the airgap H of this magnet there are formed a number of tongues l2 protrudingfrom one of the magnet poles and a number of similar tongues 72Aprotruding from the other magnet pole. The two sets of tongues 32 and HAextend toward each other as shown in Fig. 16, and each tongue I2 on onepole of the magnet has a counterpart 'iZA oppositely disposed on theother pole of the magnet. Between each adjacent pair of tongues I2 thereis formed a space 73 large enough to accommodate the galvanometer polepiece I4; and pole piece I5 will be located between the oppositeadjacent tongues 12A. The bases of pole pieces I4 and I5 rest on ledgesl6 and ISA respectively attached to the respective poles of the magnet.A number of the galvanometers may thus be placed side by side with theirpole pieces I4 and I5 located within respective opposite spaces I3 and73A.

The pole pieces I4 and I5 are adapted to fit snugly within theirrespective spaces i3 and 13A and may be moved somewhat relative to thetongues in a vertical plane; that is, the galvanometer may be tiltedback and forth to adjust the tilt of the mirror 21 somewhat so that thevertical level of its reflected light beam may be adjusted somewhat. Toprovide for this adjustment there is provided at the back of each spaceI3 and 13A an adjustable cam, the cams back of spaces 13 being numberedI4 and the cams back of spaces 13A being numbered 14A. Each adjustablecam is attached to a screw head I5, so that by turning the screw the camis turned. By turning corresponding opposite pairs of cams I4 and 74A inthis manner, accurate adjustment of the tilt of the galvanometer is had,while still maintaining good magnetic contact between-the poles of themagnet and the pole pieces I4 and I5.

An advantage of interleaving the pole pieces I4 and I5 with the tongueson'the magnet is to obtain a maximum of magnetic energy transfer fromone to the other to increase the efficiency of the magnetic circuit. Inshort, the contact area between the pole pieces and magnet is greatlyincreased by the interleaved tongue. This increased contact area morethan compensates for the loss in efficiency of the magnetic circuitresulting from the small air gap between the pole pieces and the magnet.

Ordinarily, after the galvanometer is assembled, the protruding rod 35will be cut on"; at point 76 flush with the end of member 3 I.Attachment may then be made to this terminal of the gal vanometer byclipping a wire to member 3 I. Attachment to the other end of thegalvanometer is made at the permanently connected wire 84, as describedabove.

It will be recognized that by virtue of the cone struction'andarrangement of the galvanometer, there is provided by my invention anexceedingly small and lightweight device capable of accurate adjustment.

The construction is simple for the additional reason that the entiremechanical oscillatory arrangement rotates on the axis of the supportingwires 2i and 22, making it in effect a single axis galvanometer.

' The arrangementhas the advantage over most other galvanometers or"this type in that in the present galvanometer; the electrical circuit isen tirely insulated from the casing so that the galvanometer neednothave one side grounded if grounding is not desired.

' By reason of the slidable member M, the natural period of theoscillatory coil and mirror system'may readily be adjusted, which is afactor of great convenience and desirability in such an instrument.

An outstanding advantage of the galvanometer is that the adjustment oftilt of the mirror, that is, the direction of the reflected light beam,may be made Without affecting the magnetic circuit. Regardless of theadjustment due to the cams I4 and 14A, the pole pieces I4 and I5 arealways held firmly between the tongues of the magnet, and the adjustmentdoes not affect or alter the magnetic circuit. This is a distinctadvantage over prior known constructions wherein such adjustments ofposition have involved the alteration of an air gap in the magneticcircuit, thereby affecting the strength of the magnetic circuit andaccordingly affecting undesirably, the constants of the galvanometer.

The whole assembly is of such small dimensions that a large number ofthem can be used in a portable recording oscillograph, each assemblyhaving the sensitivity usually associated with stationary laboratoryoscillographs.

The whole coil and mirror assembly is of symmetrical design about theaxis of rotation so that it does not respond to external mechanical;

shock.

passing under the fillet, the supporting wires being stretched apart intension, the respective ends of the coil being wrapped around therespective loop of the supporting wire and electrically connected to thesupporting wire.

2. An ungrounded galvanometer comprising an elongated casing, a pair ofmagnet pole pieces set through opposite sides of the casing and definingan air gap within the case, a coil of wire in the shape of an elongatedloop suspended within the air gap, a pair of supporting wires of largerdiameter than the coil wire attached on each end of the loop andelectrically connected thereto, retaining means mounted in one end ofthe case and insulated therefrom for holding one of these supportingwires, a coil compression spring located at the opposite end of the caseand insulated from the case with its longitudinal axis coaxial with thelongitudinal axis of the wire coil, a non-conductive retainer wedged inthe case for holding the spring in the end of the case, hook meansattached to the other of the supporting wires for hooking it to the endof the coil spring remote from the wire coil, thereby compressing thespring and tensioning the supporting wires, and means for makingelectrical connection to the retaining means and coil spring, said lastnamed means being insulated from the case.

3. An ungrounded galvanometer comprising an elongated-casing, a pair ofmagnet pole pieces set through the opposite sides of the casing with anair gap therebetween, a coil of wire in the form of an elongated looplocated within the air gap, a

pair of supporting Wires of larger diameter than the coil wire attachedat each end of the loop and connected With a respective end of the coil,a mirror attached to one of the supporting wires, a support affixed toand insulated from one end of the galvanometer, one of the supportingwires being fastened to said support at the longitudinal axis of thegalvanometer, a coiled spring coaxial with said longitudinal axis nearthe other end of the galvanometer, and the other supporting wire beinghooked to said spring to maintain the wires in tension, means for makingelectrical connection to the two supporting wires, said supporting wiresbeing insulated from the case and from each other so that thegalvanometer is ungrounded, and a sliding sleeve located within thecasing near the wire holding support and provided with a longitudinalslot with a protuberw ance over which the wire extending from the'sup-.port to the coil rests, said protuberance being positioned to maintainthe wire along the longitudinal axis, said sleeve acting as anadjustable slider to vary the total efiective length of the wires.

4. A galvanometer comprising a pair of magnet pole pieces with an airgap therebetween, a coil of wire in the form of an elongatedloop-located in said air gap, a pair of wires supporting the coil withone of the wires attached at each end of the loop, a support amxed toone of the casings, one of the supporting wires being fastened to saidsupport, and a sliding sleeve located within the casing near the wiresupport and pro: vided with a longitudinal slot with a protuberance overwhich the wire extending from the support to the coil rests, saidprotuberance being positioned to maintain the wire along thelongitudinal axis, and the sleeve acting as an adjustable slider to varythe total effective length of the wires.

5. Means for supporting a coil in the form of an elongated loop in acasing so that it can undergo rotary oscillation about its longitudinalaxis, comprising a fillet in each end of the loop, a pair of supportingwires, each supporting wire having a loop passing through the fillet,the respective ends of the coil being wrapped around the respective loopof the supporting wire and electrically connected to the supportingwire, a support affixed to one end of the casing, one of the supportingwires being fastened to said support, and an adjustable slider withinthe casing near the Wire support and in contact with the wire extendingfrom said support to the coil, said slider serving to vary the effectivelength of the wires.

' ARTHUR D. RICHARDSON.

REFERENCES CITED The following references are of record in the 7 file ofthis patent:

UNITED STATES PATENTS

